In the production of paper and other industrial processes, woven and spiral link belts are often utilized to transport materials through the process. In papermaking, fabric belts have become highly specialized and different constructions are utilized in the several process stages. This invention is mostly directed toward fabric belts utilized in the dryer section of papermaking machines. This is where the pulp sheet is transported at high speed and held against steam heated rolls by the dryer belt or fabric. These fabric belts are still often called felts from their historical background, even though felts have long since been replaced by technically designed fabric constructions.
As the drying pulp sheet moves through this process section, it is transformed from a wet, delicate, low strength sheet into a full strength dried paper product. The dryer fabrics used at the input end of the process are exposed to more steam and lower temperatures than fabrics used at the output end of the process. These two conditions cause there to be a need for different fabric permeabilities and different fabric materials at the several dryer stages. There is a whole industry dedicated to supplying warp and weft fibers designed for fabrics used in papermaking and industrial production.
Most modern paper machine fabrics are constructed with thermoplastic warp and weft fibers made from materials stabilized against heat and humidity. Warps are usually round or ribbon shaped, while wefts are mostly round or of twisted filament construction. Warp fibers run in the machine direction and have few twisting forces during fabric onstruction. Weft fibers run in the cross machine direction and in most constructions have twist imparted into them during fabric weaving. There have been recent developments of hollow and shaped fibers targeted for use in dryer fabrics. Cost of the thermoplastic materials used to produce these fibers is an important consideration in fabric production.